類型安全的事件系統實現

Question

我爲我的遊戲寫了一個事件系統。它工作正常，但有一個很大的缺陷 - 它不是類型安全的，因此需要訂閱的回調函數手動強制接收基本事件。現在，我正在嘗試使用模板實現類型安全版本。我通常對這個話題很滿意，但顯然不是專家。

首先，這裏是一些代碼演示如何我想使用的事件：

定義的衍生事件

// Derived Events 
class ClickEvent : public Event 
{ 
public: 
    float x; 
    float y; 
}; 

class RenderNodeCreatedEvent : public Event 
{ 
public: 
    unsigned long long int renderNodeId; 
}; 

創建它們並（在主程序例如用於測試目的）使用它們

// Create the on event functions 
std::function<void(const ClickEvent &)> onClickFunction = [](const ClickEvent & event) 
{ 
    std::cout << std::endl << "Mouse clicked at position: " << event.x << event.y; 
}; 

std::function<void(const RenderNodeCreatedEvent &)> onRenderNodeCreatedFunction = [](const RenderNodeCreatedEvent & event) 
{ 
    std::cout << std::endl << "Render node created with id: " << event.renderNodeId; 
}; 

// Create the events 
ClickEvent clickEvent; 
clickEvent.x = 300.f; 
clickEvent.y = 255.5f; 

RenderNodeCreatedEvent renderNodeCreatedEvent; 
renderNodeCreatedEvent.renderNodeId = 26234628374324; 

// Create the event manager and subscribe the event functions 
EventManager eventManager; 
eventManager.Subscribe(onClickFunction); 
eventManager.Subscribe(onRenderNodeCreatedFunction); 

// Raise the events 
eventManager.Raise(clickEvent); 
eventManager.Raise(renderNodeCreatedEvent); 

這是我試圖產生std::size_t類型的唯一ID爲每個派生事件類：

class BaseEvent 
{ 
public: 
    typedef std::size_t ID; 

    BaseEvent() = default; 
    virtual ~BaseEvent() = default; 

protected: 
    static ID GetNextID() 
    { 
     static ID id = 0; 
     return id++; 
    } 
}; 

class Event : public BaseEvent 
{ 
public: 
    Event() = default; 
    virtual ~Event() = default; 

    // Sets a unique id for the event the first time this function is called 
    ID GetID() 
    { 
     static ID id = BaseEvent::GetNextID(); 
     return id; 
    } 
}; 

最後，這是我的（可怕的）嘗試在事件管理器，可以提供上述功能。我非常努力地管理正確的投射和/或存儲不同類型的回調函數。回調包裝器不起作用 - 它只是一個基本的想法，我必須解決這個問題，所以我把它包含在帖子中。

class EventManager 
{ 
public: 
    // Define the template callback type 
    template <class DerivedEvent> 
    using TCallback = std::function<void(const DerivedEvent &)>; 

public: 
    EventManager() = default; 
    ~EventManager() = default; 

    template<class DerivedEvent> 
    void Subscribe(TCallback<DerivedEvent> callback) 
    { 
     // Get the index of the callback list this callback will be added to 
     Event::ID id = DerivedEvent::GetID(); 

     // This won't work sinve TCallback is a different type than TCallback<Event> 
     callbackListList[id].push_back(callback); 
    } 

    template <class DerivedEvent> 
    void Raise(DerivedEvent event) 
    { 
     // Get the type of the event and therefore the index in the callbackListList 
     Event::ID = DerivedEvent::GetID(); 

     /// How to cast the events back 
     // Get the respective list of callback functions 
     std::vector<TCallback<DerivedEvent>> /*&*/ callbackList; 

     // Create a callback wrapper of with the type 'derived event' ????? 
     CallbackWrapper<DerivedEvent> callbackWrapper(/*derived callback*/); 
     // Call the callback wrapper using the base event ????? 
    } 

    template <typename DerivedEvent> 
    class CallbackWrapper 
    { 
    public: 
     CallbackWrapper(TCallback<DerivedEvent> callback) : callback(callback) {} 

     void operator() (const Event & event) 
     { 
      callback(static_cast<const Event<DerivedEvent> &>(event).event); 
     } 

    private: 
     TCallback<DerivedEvent> callback; 
    }; 

private: 
    std::vector<std::vector<TCallback<Event>>> callbackListList; 
}; 

我知道這是很多代碼，但我覺得這是展示我所談論的最簡單的方法。

感謝您的幫助，阿德里安

編輯： 事件類都必須聲明爲模板，以獲得唯一ID派生類型。現在

template <class DerivedEvent> 
class Event : public BaseEvent 

從事件繼承時：

class ClickEvent : public Event<ClickEvent> 
class RenderNodeCreatedEvent : public Event<RenderNodeCreatedEvent> 

最後，eventmanager進行只能存儲類型的回調的矢量的矢量BaseEvent

private: 
    std::vector<std::vector<TCallback<BaseEvent>>> callbackListList; 

Answer 1

長一些研究之後，我發現這篇文章基本上解決了ECS事件/信使實現問題：

https://codereview.stackexchange.com/questions/79211/ecs-event-messaging-implementation